question about multi gang capacitors

Why are many multi gang air variable tuning capacitors made with different max and mins for each section?

George

My guess would be because they are tuning different frequency circuits. One will be the RF front end, the other will be th local oscillator which will be a different frequency.

Keith

Thank you, that is very helpful. I am trying to design a "zero IF" direct conversion receiver, so if I am not mistaken I will be better off with a tuning cap where the gangs were equal. I know they exist, but I am having trouble finding one. Does anybody know where I can get one?

It is a long shot, but Jackson used to be the main manufacturers a long time ago http://www.mainlinegroup.co.uk/jacks...hers/index.htm

Keith

Today I assume nobody makes such variable capacitors as they are no more used commercially. You can get some at radio-amateur swap meets.
A good option is to use varicap diodes. Some manufacturers even sell matched quads, or, buy more and select matching groups. Instead of mechanical coupling you will tune all by one potentiometer.

One section is for AM and the other for FM.

These days it's probably easier to make your own tuning cap than to try and buy a decent one.

Here's a couple of practical approaches:
http://www.sm0vpo.com/use/tuning_caps.htm
http://www.sm0vpo.com/use/tuning_caps2.htm

Googling "DIY tuning capacitor" will probably bring up some other ideas too.